PURPOSE: To improve the tracking of a segment and the performance of line kind decision based upon the tracking by accurately continuing the tracking of the segment and efficiently grouping vectors as one line in a line kind recognizing method for an automatic drawing input device to be used for a CAD.

CONSTITUTION: In a vector sorting process 1, a threshold is set up in the 'length' information of a core vector to be recognized and a vector shorter than the threshold is set up as a 'point', while sorting a longer vector as a 'line'. When the 'point' is selected as a connection candidate in a segment tracking process 2, a segment is supposed between the 'point' and a tracking reference point to be a reference vector and the segment is tracked as the directional vector of the 'point'. In a line kind deciding process 3, the segment is recognized in accordance with the tracking.